Heat exchanger



w. A. SPOFFORD 5 HEAT EXCHANGER Filed April 25, 1941 H is AttormeyPatented Aug. 25,1942

nanrnxcr Warren A. Spofi'ord, Glen Ridge, N. 3., assignor to GeneralElectric Company, a corporation of New York Application April 25, 1941,Serial No. 390,363

5 Glaims. (ill. ldS-d) M invention relates to heat exchangers and moreparticularly to heat exchangers having relatively thin walls which aresubject to distortion caused by internal pressures.

This is a continuation-m-part of my copending application, Serial No.323,219, filed March 9, 1940, and assigned to the same as'signee as thepresent invention.

It has been proposed to constructheat exchangers in which the fluidconveying tubes are formed from relatively thin metal. It has also beenproposed to provide some sort of internal stay for such tubes. Thus, ithas been proposed to provide flat tubes with pins or rods extendingthrough opposite walls of the tube, the pins or rods acting as heatexchange members, and also stay members to prevent such distortion. Withsuch a construction, it is necessary to secure the members to the wallsof the tube at the two places where each wire passes through the tube,or if the through type member is not used to secure the ends of aninternal heat exchange and stay member to the opposite walls. When themembers are soft soldered, it is usually possible to make the jointwithout annealing the wires but whenever it is necessary or desirable tosecure the members by a relatively high temperature securing operationas silver soldering or brazing,

the members may be annealed at the soldering temperatures. tensilestrength of all cold-worked ductile metals is reduced by annealing sothat whenever the material utilized for the fins and stay members ortubes or both anneals at the securing temperature or lower, thestructure is weakened when the parts are so secured. In order to restorethe strength to the fins after the securing operation, or to increasethe strength of the assembly, I cold work the fins or tube walls or bothby stretching. The cold working step must be carried out at atemperature below that at which recrystallization takes place. Forexample, copper, which is commonly used for the aforementioned purposesbecause of its relatively high heat conductivity and corrosionresistance to water, becomes annealed at about 400 C. and since thetemperature of brazing is about 750 C., the fins become annealed duringthe brazing operation. Recrystallization takes place at about 200 C. sothat the cold working step is carried out below this temperature. Roomtemperature is satisfactory for this step.

Accordingly, it is an object of my invention to assemble a heat exchangeelement in a manner to restore the strength of the heat exchange and Itis known that the ultimate stay members which have been weakened byannealing.

Even when the heat transfer members are not annealed during the assemblyprocess, it may be desirable to strengthen the members or fins bycold-working. Therefore, it is another object of my invention toassemble a heat exchange element in a manner to increase the strength orthe heat transfer members.

It is another object of my invention to provide a new and improved heatexchange element and a new and improved method for constructing thesame.

Still another object of my invention is to in= crease the strength ofexternal heat transfer members or the external portions of heat transfer members whenever such a result is desired.

Further objects and advantages of my invention will become apparent asthe following description p'roceedsancl the features of novelty whichcharacterize my invention will be pointed out with particularity in theclaims annexed to and forming a part of this specification.

For a better understanding of my invention, reference may be had to theaccompanying drawing in which Fig. l is a side elevational partial viewof a heat exchanger embodying the principles of my invention; Fig. 2 isa perspective exploded view of a portion of a heat exchanger and theapparatus used in forming heat exchange elements of the type illustratedin Fig. 1; Fig. 3 is a cross-sectional view of the apparatus shown inFig. 2 preceding the operation of cold working the heat exchangeelement; and Fig. 4

l is a view similar to Fig. 3 illustrating the heat exchange elementafter the cold working opera- 7 tion.

In the drawing I have illustrated a heat exchange element comprising afluid conveying conduit Ill and a plurality of heat exchange members orfins I I formed from a material having relatively good heat conductivityand extending through opposite walls of the tube it. In order to permitcold working of the members it following brazing or silver-soldering tothe tube H) at the points of passage through the walls thereof, I spacethe two sides or walls I2 and I3 of the tube I0 nearer together duringthe operation of soldering or brazing the members to the walls than isultimately desired. The flanged T ture members l4 and I5 and hydraulicpressure is applied to the interior or the tube III in order to forceapart the walls l2 and I3 oi the tube thereby cold working by stretchingthe wires or pins li a predetermined amount, thereby providing acombined stay and fin member which has been strengthened by cold workingafter having been secured in position.

Describing my invention in greater detail I have shown in Fig. 1 aplurality. of fluid conveying tubes In communicating at opposite endswith headers l8 and I1 and having heat exchange members or fins II. Theheat exchanger is enclosed in a suitable casing l8. Thus, a heatexchange fluid, ,such as water, may enter the heat exchanger, as acondenser, for example, at the header l8, and flow through the tubes linto the header l1 irom which the fluid may be discharged. If the heatexchanger is being used as a condenser, the fluid to be condensed willbe passed across the outside of the tubes in contact with the tube l0and the fins H.

In Figs. 2 to 4, inclusive, 1 have illustrated suitable apparatus forobtaining the aims of my invention. In order to render the tubes l0fluidtight, the pinsor fins II are silver soldered or brazed at thepoints of passage through the walls l2 and I3, as previously described.As

illustrated, the walls I 2 and I3 are spaced apart but in order to forma complete tube the members l2 and I3 have been provided with side wallportions l9 and 20 and longitudinally extending marginal flanges 2| and.22 for securing purposes. Following the attachment or the pins or rodsII, the flanges 2| and 22 are secured together in fluid-tightrelationship as by soldering or welding. In order to render the ends ofthe tubes fluid-tight I have provided suitable plugs 23 and 24, thelatter being provided with a suitable connecting member 25 forconnection with a supply of suitable fluid.

. In order to limit the expansion of the -walls of the tube l0 and theportions 26 of the wires or pins H to a uniform degree and apredetermined amount I have provided a suitable fixture comprisingelements I4 and I5. elements or members I4 and I5 is recessed asindicated by the numeral 21, to receive the oppositely disposed walls l2and I3 of the member ID. The recessed portions 21 are dimensioned topermit the walls I2 and I3 to be forced apart to the ultimately desireddimension. In order .to secure the members l4 and I5 together andprevent them from being forced apart I have provided the member l5 witha plurality of threaded members 28 arranged to extend through suitableopenings 29in the upper member l4 and engage threaded fastening membersor nuts 30.

Whenever the fluid conveying tubes III are provided with external finsit is necessary to provide corresponding depressions or openings in thewalls of the members l4 and I5 communicatlug-with the recesses 21. Thus,in the pin type heat exchanger illustrated in the drawing I have,

provided openings 3i extending entirely through the members I 4 and I5.

In Fig. 3 there is illustrated the arrangement of the apparatus afterthe heat exchanger has been placed between the members I4 and I5 and thenuts 30 applied to the members 28. It will be observed that the walls [2and I3 are spaced from the corresponding walls of the members l4 and I5,respectively. In Fig. 4, there is illustrated the heat exchanger of Fig.3 after the Each of the application of fluid pressure to the interior ofthe tube In illustrating the walls of tube ID in their forced-apartcondition, the portions 26 of the pins ll having been stretched. Thenuts 30 are preferablyloose enough to permit relative movement betweenthe longitudinally extending side flanges of the tube l0 and thesurfaces 32 and 33 of the members 14 and I5, respectively.

I have found that if walls 12 and i3 of copper are spaced apart adistance of one-half an inch before the application of the hydraulicpressure, the ultimate strength of pins ll of copper may be increasedapproximately 22 per cent by an elongation of the pins of- 55 of aninch. Not only .will the pins I I be cold worked but the edges or sidewalls of'the tube ID will also be cold worked adjacent the flangesthereby restoring or increasing the strength of the tubes l0 adjacentthe aforementioned flanges.

Many modifications of my invention will be apparent to those, skilled inthe art. For example, threaded members such as 28.and nuts 30 need notbe employed. Any arrangement for maintaining the blocks H and IS in aposition for permitting expansion of the tube In to itsultimatelydesired position will be satisfactory. Moreover, any arrangements forsealing the ends of the tube during assembly may be employed.

In the practice of my invention a fixture is not essential, althoughconvenient. Another method of accomplishing the desired purpose would beto stretch the wires by mechanical means before the tube walls arewelded or brazed together. This method would also increase the strengthof the pins ll externally of the tube In.

My invention is not limited to a particular type of fin but isapplicable wherever internal stays may be used, wherever it is desirableto utilize a fln or stay member to reinforce a conduit againstdeformation from pressure on one or the other side of the fluidconveying tube, or wherever it is desirable to increase the strength ofexternal or internal fins after assembly.

While I have shown a particular embodiment of my invention, I do notdesire my invention to be limited to the particular construction shownand described and I intend in the appended claims to cover allmodifications within the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. The method of forming heat exchange elements of the type having arelatively thin-walled conduit with members disposed internally thereofand serving not only to transfer heat between a fluid flowing in saidconduit and the conduit Walls but also to reinforce the conduit walls,comprising the steps of spacing two conduit wall members nearer togetherthan ultimately desired, providing heat transfer elements of a materialhaving relatively good heat conductive properties and which is weakenedby annealing between said walls, securing said elements to said walls ata temperature above the annealing temperature of said material, securingtogether adjacent marginal edges of said walls to provide a fluid-tightfluid conveying tube and moving apart said wall members into theultimately desired positions at a temperature less than the temperatureof recrystallization of the material of said elements thereby coldworking said elements by stretching whereby said elements arestrengthened.

2. The method of forming heat exchange elements of the type having arelatively thin-walled and applying fluid pressure to the interior ofconduit with members disposed internally thereof and'serving not only totransfer heat between a fluid flowing in said conduit and the conduitwalls but also to reinforce the conduit 'walls comprising the steps ofspacing two conduit wall members nearer together than ultimatelydesired, providing heat transfer elements of a material havingrelatively good heat conductive properties and which is weakened byannealing between said walls, securing said elements to .said walls at atemperature above the annealing tempera- ,ture of said material,securing together adjacent marginal edges of said walls to provide afluidtight fiuid'conveying tube and applying fluid pressure to theinterior ofsaid tube for moving apart said wall members into theultimately desired positions, thereby cold working said elements bystretching whereby said elements are strengthened, said cold workingstep being carried out at a'temperature less than the temperature ofrecrystallization of the material.

3. The method of forming heat exchange elements of the type having arelatively'thin-walled conduit with members disposed internally thereofand serving not only to transfer heat between a fluid flowing in saidconduit and the conduit walls but also to reinforce the conduit wallscomprising the steps of spacing two conduit wall members nearer togetherthan ultimately desired providing heat transfer elements of a. materialhaving relatively good heat conductive properties I and which isweakened by annealing between said walls, securing said element to saidwalls at a temperature above the annealing temperature of said material,securing together adjacent marginal edges of said walls to provide afluid-tight fluid conveying tube, providing a fixture having said tubefor moving apart said wall members into the ultimately desired positionand also cold working said element by stretching whereby said elementsare strengthened to resist distortion of said wall members from internalpressure, the cold working step being carried out at a temperature lessthan the temperature of recrystallization of the material.

'4. A heat exchange element having a thinwalled fluid conveying conduitwith members formed from a material having relatively good heatconductivity and which is weakened by annealing disposed internallythereof for transferring heat between afluid flowing through saidconduit and said conduit walls and also for reinforcing said conduitwalls, said members being secured between opposite walls at atemperature above the annealing temperatures of said material, saidmembers also having been strengthened by moving apart said oppositewalls from a first position into the ultimately desired position, saidstrengthening step being carried out below the temperature ofrecrystallization of said material.

5. A heat exchange element having a thinwalled fluid conveying conduitof copper with copper members disposed internally thereof fortransferring heat between a fluid flowing through.

said conduit and said conduit walls and also for reinforcing saidconduit walls, said members having been secured between opposite wallsat a temperature above the annealing temperature of copper, said membersalso having been strengthened by-moving apart said opposite walls at atemperature below the temperature of recrystala recess, the walls of therecess being spacedapart a distance equal to the ultimately desiredspacing of the conduit wall members, placing the assembled tube andmembers in said fixture lization of copper from a first position intothe ultimately desired position thereby cold working said members.

WARREN A. SPOFFORD.

